1. Field of the Invention
The present invention relates to a control system mounted on a vehicle, and in particular, to a real-time control system provided with a plurality of ECUs (electronic control unit) performing real-time control for the vehicle based on time-dependent data transmitted and received between the plurality of ECUs.
2. Description of the Related Art
There has been a conventional system in which a plurality of ECUs (electric control unit) are mounted on a vehicle and time-dependent data is transmitted and received between the ECUs via signal lines such as an in-vehicle LAN, and this transmitted/received time-dependent data is used as a basis to achieve one of the vehicle real-time controls. The time-dependent data refers to data that consistently changes based on the vehicle running condition and condition outside the vehicle. The real-time control refers to control under which the time-dependent data for use in the control is ideally an amount dependent on the instant time at which the control is actually performed in sequence.
Examples of such a system include an auto cruise control system (Auto Cruise Control). In the auto cruise control system, a forward-obstacle identification system such as a laser-radar sensor first feeds to the inter-vehicle distance control ECU a signal indicating spacing to the preceding vehicle and others. The inter-vehicle distance control ECU then uses this fed signal as a basis to compute a target running speed for keeping a proper distance between the vehicles, and outputs computed result signals to an engine ECU. The engine ECU, to run the vehicle at the target running speed of the received signal, determines operation contents of actuators, such as the electronic throttle, injector, and ignition plug, and then controls these actuators according to the determined results. The target running speed data for use in the actuator control is ideally an amount based on the inter-vehicle distance at the control time.
In such a system which uses the time-dependent data transmitted and received between a plurality of ECUs as a basis for the vehicle real-time control, if the time-dependent data is not transmitted and received within a proper time and is delayed, the control may be performed based on the time-dependent data at the old time, and a large difference may occur between the actual-control time and the time of the time-dependent data for use in the control, as a result of which mismatching may occur in the vehicle real-time control.
In the adaptive cruise control system as mentioned above, for example, if a large difference exists between the time at which the forward-obstacle identification system detects the distance to the preceding vehicle, and outputs it and the time at which the engine ECU uses this detected distance as a basis to finally control the actuators, the vehicle has to control the vehicle-running speed and other parameters based on a considerable-previous inter-vehicle distance, thereby making it difficult to keep the proper inter-vehicle distance.
The time-dependent data between ECUs are not transmitted or received within a proper time and are delayed in cases in which, for example, (1) the data is transmitted and received via an in-vehicle LAN that is busy for other data transmissions, and (2) any of ECUs that transmits and receives data has to process a large amount of data such as image, so that the relevant ECU has more processing load and the time-dependent data transmitted and received is sent and received in a delayed manner.
To decrease such mismatching in the vehicle real-time control, it is preferable that among the time-dependent data transmitted and received between ECUs, the time-dependent data transmitted and received within a proper time is differently treated from the time-dependent data that is not transmitted and received within a proper time.